1. Field of the Invention
The invention relates to methods of treating arthritic diseases and associated inflammatory diseases.
2. Description of the Prior Art
Arthritic diseases are characterized by joint inflammation, although the etiology of the inflammation may differ in various conditions. Relatively common arthritic diseases include rheumatoid arthritis, juvenile arthritis, ankylosing spondylitis, psoriatic arthritis and osteoarthritis, often referred to as degenerative joint disease.
Most forms of arthritis are treated initially with nonsteroidal anti-inflammatory drugs, sometimes together with other analgesics. Where the disease is not adequately controlled with these agents, disease-modifying (remission-inducing) antirheumatic drugs, such as gold salts, D-penicillamine, antimalarial agents and cytotoxic agents, may be utilized. Ultimately, glucocorticoids may be administered, systemically or by the intra-articular route. None of these drugs is significantly effective in achieving true remission of the disease in most patients.
Moreover, all of the currently practiced drug treatments for arthritic diseases have significant drawbacks. Apart from gastrointestinal disturbances, the nonsteroidal anti-inflammatory drugs may cause renal dysfunction in susceptible individuals. The antimalarials may cause serious retinopathy which can occur several years after initiation of therapy. Chronic glucocorticoid therapy is associated with a number of pernicious side effects, including hypertension, adrenal suppression, excessive immunosuppression and CNS dysfunction. Immunosuppressive and cytotoxic agents can cause bone marrow depression and lead to serious infection.
The inflammatory process is mediated by a variety of endogenous substances which can be categorized as follows: vasoactive substances, chemotactic factors, and agents causing cell and tissue damage. Among the vasoactive substances are histamine, serotonin, protein constituents of the complement system, bradykinin, and prostaglandins. Prostaglandin levels are increased in the synovial fluid of patients with rheumatoid arthritis and osteoarthritis. All effective nonsteroidal anti-inflammatory drugs inhibit prostaglandin systhesis, thereby reducing the concentration of prostaglandins. See generally American Medical Association Drug Evaluations (6th ed., 1986), p. 1049.
Tissue damage in inflammatory diseases results from the complex interplay of humoral and cellular immune responses. In rheumatoid inflammation, antigen-antibody complexes accumulate in synovial tissues and activate the complement system, leading to the release of inflammatory mediators, including lysosomal enzymes, prostaglandins, and free oxygen radicals. It has been hypothesized that many of the manifestations of joint damage occurring in arthritis could be the result of damaging free oxygen radicals, large amounts of which are released together with powerful digestive enzymes into the arthritic joint by polymorphonuclear leukocytes undergoing "frustrated phagocytosis." These radicals have been shown to degrade DNA and hyaluronic acid, a major constituent of synovial fluid, and, to some extent, to degrade also collagen and elastin. Moreover, oxidants can activate latent collagenase, possibly by inactivating protease inhibitors, leading ultimately to cartilage destruction.
It is known that inflammatory cells such as polymorphonuclear leukocytes have opiate receptors. The endogenous opioid B-endorphin has been shown in vitro to stimulate superoxide radical production by human polymorphonuclear leukocytes via an opiate receptor. This superoxide production has been shown to be abolished by equimolar concentrations of the opiate antagonist naloxone. B. M. Sharp et al., J. Pharm. Exp. Ther., 242(2):579-582 (1987). Naloxone has also been shown to inhibit in vitro the production of superoxide from human neutrophils stimulated with N-formyl-methionyl-leucyl-phenylalanine, which effect is not opiate receptor-mediated, nor is it the result of superoxide scavenging. Simpkins et al., Life Sciences, 37:1381-1386 (1985).
Systemically-administered naloxone has been shown to exert tissue-protective effects in a variety of experimental and clinical conditions in which the damaging effects of superoxide radicals and their derived oxygen species (hydrogen peroxide and the hydroxyl radical) are believed to play a major role. In particular, naloxone has been recently shown to have a protective effect on the ultrastructure of the ischemic canine kidney. H. K. Elkadi et al., J. Surg. Res., 42:675-692 (1987).
Despite the foregoing, neither naloxone nor any other opioid antagonist has been disclosed heretofore as clinically useful in the treatment of the inflammatory manifestations of arthritic diseases. There has also been no suggestion that such antagonists might not only relieve inflammation but also cause true remission in such diseases.